Traveling wave electron discharge devices



April 9, 1957 R. H. GEI'GER TRAVELING wAvE ELECTRQNI'DISCHARGE DEVICES Filed oct, 29, 1.954`

3 Sheets-Sheet l Nmwo INVENTORf RICHARD fn 62765K BY g7 ATTORNEY April 9, 1957 R. H. GEIGER 2,788,464

TRAVELING WAVE ELECTRON DISCHARGE DEVICES Filed oct. 29. 1954 l 3 Sheets-Sheet 2 SOURCE 26 +P 83 6 l i 24 Q l ,/t 2 7 Q INVENTOR R/c/mo fn ff/G5@ BY @fw ATTORNEY April 9, 1957 2,788,464 TRAVELING WAVE ELECTRON DiscHARGE DEVICES Filed oct. 29, 1954 R. H. GEIGER :s shets-sheet. s

. INVENTOR ,Q/cwA/Qa Af .Gf/i@ BY z Z g;

ATTORNEY United States. Patent O TRAVELING ELE'CVTJRN DISCHARGE' DEVISES Richard. H. Geiger; Emerson, NL J., assigner to International Telephone i andfg'ilelegraphf Corpuration, lEJuticy, N. I., acorporationroMarylaud.

Application-Gctbher'29, i954, Serial No2 465,513`

18 Claims. (Cl. 3153.5)

This invention'` relatesy tolV traveling wave. electron' discharge devices and more. particularly to gas discharge devices for introducing a` circuit loss along the path; of a. traveling wave in such` electron discharge devices to prevent both undesirable oscillations and propagating modes.` therein.

In the. traveling wave type of tube.- for amplitication in wideband microwave systems, the useful range of amplification which can beiutilizedis limited by a tendency togener-ate self-sustained oscillations asn the arnplification isl increased. This effect is` usually due to mismatch between.` the output circuit of the device and the load circuit` over all or parti of the wide range of frequencies to beV amplified.. Due tov suchI mismatch, energy of` at` least certain frequencies is reflected back toward, the input endf of the. amplifying device. When the reflected wave is` not. 'attenuated in` its travel in` a direction opposite: to. the motion of. the electron: stream, some energy reaching the. input end of the` device. is` reflected from the input endA causing. the.` generation` of self-sustained. oscillations. Thus,.the energy reflected or transmitted back to the input end must. be attenuated if the tube is to remain. stable.`

In most traveling wave devices heretofore proposed, particularly the helical. transmission line type,` attempts have been` made to overcome this tendency of generating self-sustained oscillations byy employing resistivel or lossy material to` attenuate the. reflected waves. The distribution ofthe resistivematerial along the entire lengthof the helix,y along4 a major portion thereof, in lump form, or asa part of the helical conductor itself limited the gain and-.power output ofthe device. Where the resistive material is spaced from the conductor such= as in` the lumped form,` it is less effective and requires a` larger amount ih order to absorb the reected energy. Further, the utilizationof anrorganic lossmaterial, such as carbon, or aquadag, malies the out-gassing of the traveling wave device more difficult since the organic material entraps more gases than wouldl normally be, found when the organic material is omitted;

lt is an object of the present invention, therefore, to provide an improved'` means for introducing a circuit loss in theV path of the radio frequency Wave of a trave1- ing wave device so as to prevent self-sustainingy oscillations and yet obtain high gain and maximum. output power.

It has been discovered that in. one approach to obtain high gain and maximum power output that the attenuating means must be concentrated' within the smallest axial length of theA helix possible and with proper impedance match. The conductivity of the helical conductormust be maintained high, the input section of the helix' must be as lossless as possible and sufficiently long to enable the gaining wave of the energy launched on the prepau gating structure to achieve a sufficient amplitude andthe output section of the helix must also be lossless and as long. as permissible for: achievement of thel desired gain and power output. It is, therefore, another object of Patented: Apr. L i915?? 2. this invention to' provide the; wave? propagating structure of a, traveling wave` device.` with; an: attenuator havingv the relationship and soA disposed relative: to the` propagating structure` to` satisfy the above-mentioned requirements which have: be'euxfounddesirable for high; gain.i and max-rmum power output.

One' of. the features: offthis invention i's theutilnation of. a: gaseous discharge device: having an electronw density. upon, ionization such. that. the` collision: frequency ofthe electrons therein is. approximately' equal to the angular frequency ofthepropagjating microwaveA energy to intel?- ccptpart of thel highs` frequency field ofy the. propagated energy with at minimum 0f. reflection! or. radiation of the radio'frequency energy and Whiehfwill. absorbW the microwave energy in azminimul'trI axialfdi'stancefalong the prop agating` structure.

Another feature ofthisinvention` is theprovision` of a` gas discharge device having an envelope of annular.-like crosssection, the ends of which aretapered radially relative; to the propagating structure, disposed concentrically about` the propagating structure andV within they field.. of the microwavey energy transmittedV on' the: propagating structure.

Other fea-tures of this invention include the shaping of the envelope ofithe` gas discharge device. to position the ionized gas. within a. stronger held region of the electromagnetic field. present. about a helical propagating structure. whereby thef ionization. of. the gas. within the various shaped gaseous discharge devices may bef accom plished` by` potential difference. pulsed potential sources associated with cold cathode materiaL, andthe radio. fre quency field. of the propagated.` wave. alone` orin. cornhination` with. the. intensity of the.. longitudinal magnetic eld? present in` a= traveling wave device.. for achievement of gyroresonance.

The above-n'ientionedj` and other features and objects of this inventionwill Become more. apparent by reference to the following description. taken inn conjunction with the accompanying drawings, in which:4

Fig. 1I is)` a` diagrammatic representation. of. a.- traveling wave electron discharge device incorporating a gas dis" charge attenuat'or, in accordance withthisr invention;l

Fig. 2` is an` enlargedlongitudinal crossf section of the gas discharge device of Fig. l;

Fig. 3" i`s a. cross-sectional view taken` along. line 3--3 0f Fig. 2;

Fig, 4 is a longitudinal cross-sectional View of. another embodiment of this invention;Y

Fig. 5 is a cross-sectibnal" view taken along liner 5-.5 of, 4;'

`Figs. 6, 7,', 81 and 9 areA longitudinall crossesectional views, partially diagrammatic, of"still` other embodiments of," this invention;A and Fig. l1() is a diagrammatic illustration of a traveling wave, electron discharge device incorporating.` stillanother embodiment of this invention.

Referring' to Fig. l, there is shown an illustrative embodiment of a' discharge device' adapted to beV used as an amplifier at microwave frequencies. The. arrangement shown comprises an electron beam: tuhe including an evacuated'envelope 1. The` envelope 1 may be composed of a low-loss insulatedmaterial, such as glass or quartz, ora suitable metal havingnon-magnetic properties. The envelope 1 is provided at onel end" with al hnown type of elect-'ron gun Zlforproducihg an electron beam' or stream of either the pencil typeorhollowtype: The electron beami emerging from gurr 2" in the illustrated embodiment` is; of the pencil type and travels along a path substantially axially of. envel'opel. andpassiugsthrough input coupler 3. The; electron; stream is further concentrated andi guided paralleli to: the? airis` of envelope'l within the space surrounded by helical transmission line 4 by a lou` gitudinal magnetic field produced by apermanent magnet or an electromagnet as represented by S. Electrode 6 serves to collect the electrons arriving at the end of envelope 1 after passage through the helical propagating vstructure 4. While the propagating structure of the traveling wave tube is herein shown and described as being a helical transmission line, the propagating structure need not necessarily be limited to such a helical structure, but may include transmission lines composed of baflles and similar devices.

The helix 4 is wound to haveV a length of a plurality of wavelengths at the frequency to be amplied along its axis. The helix is supported to provide a rectilinear structure coaxial of the axis of envelope 1 by a nonconductive structure shown in this instance to comprise a series of non-conductive rods 7 equally spaced around the circumference thereof. A non-conductive tubing coextensive with the length of the helix may be substituted for the rods. The rods or tubing may be composed of a suitable ceramic material disposed between the helix 4 and the envelope 1 and positioned axially of envelope 1 by discs 8 and 9 disposed at the extremities of the helix and in a transverse relation with respect to envelope 1. The helix 4 is joined to the input coupler 3 by an input impedance matching section 10 and the output coupler 11 by the output impedance matching section 12. These matching sections are simply extensions of the helix in which the spacing between adjacent turns is increased along the circumference of the helix and act as tapered transmission lines to provide a wave transmission path of uniformly changing impedance from the relatively low impedance at the end of the couplers 3 and 11 to the relatively high impedance of the center portion of helix 4 with a minimum reflection of energy back to the signal source.

, In order to utilize the device in an operable system, lthere is provided an input wave path represented by the dotted input waveguide 13 into which there is introduced the input wave signal to be amplified. An output wave path shown as the output waveguide 14 serves to transfer the amplified output wave to a load circuit. The wave from the input waveguide 13 and coupler 3 travels along the circumference of the helix 4 at a speed approximating that of light, but at a linear velocity along the axis of thetube which approximates or is slightly slower than the velocity of the electrons of the beam. As the beam and the radio frequency wave travels along the helix, an interaction takes place whereby energy is transferred from the beam to the wave thereby greatly yamplifying the wave. It has been fairly well established in the prior art that the wave launched upon the propagating structure consists of three components, an increasing component, a decreasing component and an .unattenuated component. It is, of course, realized that the resulting amplification is accomplished by the interaction between the increasing component of the wave and the electron beam. As the amplified wave reaches the output end of helix 4, it is transferred to the output waveguide 14 by means of output coupler 11. As the amplified wave reaches the impedance matching section 12 at .the output end of helix 4, even with an extremely favorable termination, at a given band of frequencies, there will still exist reflected waves at frequencies inside and outside the given band at the output end of the helix. This reflected wave, while it does not enter into the interaction with the electron stream, is propagated back along helix 4 toward the input end with attenuation. The reflected wave will reach the input end of the helix 4 with attenuation equal to the circuit attenuation and will in turn be reflected back toward the output end of the helix. It is obvious that there will be some reflected energy which will result in self-sustaining foscillations, provided there is not enough circuit attenuation to dampen the reflected energy. The circuit attenuation in the past has been deliberately increased by the addition of an artificial loss along the helix so as to provide a dissipation of the reflected wave which served to increase the range of useful amplification. rli`he introduction of a lossy material in the form of aquadag, however, reduced the gain and power output of the traveling wave device.

In accordance with the principles of this invention, an artificial loss is introduced along a portion of the helix 4 which will increase the range of useful amplification, but which will not reduce the gain and power output of the traveling wave device. The artificial loss of this invention introduced in juxtaposition to helix 4 is provided by gas discharge device 15.

Referring to Figs. 2 and 3, a cross-sectional view of one embodiment of my gas discharge device 15 is illustrated as comprising an annular envelope 16 disposed to be in contact with the support rods or tubing 17 of the helical propagating structure 4. The inner surface of envelope 16 is brought as close as possible to the electromagnetic field present about the helix. The envelope 16 is filled with a suitable noble gas, such as helium, neon, argon, krypton and xenon, and is in some manner caused to ionize to function as an attenuator for the propagating structure of a traveling wave electron discharge device.

As is known, a gaseous discharge plasma may act as a propagating medium for microwave and if the electron density of the discharge plasma is adjusted so that the collision frequency of the electrons of the gas is approximately equal to the angular frequency of the propagating microwave energy, the plasma absorbs the microwave energy. The degree of absorption is determined by the magnitude and distribution of the electron density in the radio frequency elds. Therefore, it has been discovered that if a gaseous discharge plasma is located close to the turns of a helical structure, such as helix 4, where the electromagnetic ield distribution is at a maximum between the turns of a helix, effective absorption or attenuation will occur.

Discharge device 15 is provided with anodes 18 and 19 which in turn are placed across a potential source 20, as illustrated in Fig. l, which when switch 21 is closed, will establish a potential difference between electrodes 18 and 19 of suflicient value to ionize the gas within envelope 16 to produce a discharge plasma of sufficient electron density whose collision frequency is approximately equal to the angular frequency of the propagated energy such that an absorption or attenuation of the energy will take place. Envelope 16 is provided with ends 22 which are tapered radially with respect to the helix to reduce reflections from the glass envelope 16 and the discharge plasma.

The characteristic of the loss medium of this invention is such that most of the electromagnetic energy in the propagating structure is absorbed, and the signal is transmitted through the loss section by the modulation signal energy in the electron stream. At or near the output end of the loss section, the electromagnetic wave is re-excited in the lossless section of the propagating structure by the modulated electron beam. The location of discharge device 15 is a predetermined distance from the input end of structure 4 such that the equation CN0-3 is satisfied, where C is the gain parameter relating the degree of interaction between the electron beam and electromagnetic wave propagated along the propagating structure and N is the number of wavelengths from the input end. Provision of an input portion of helix having a length corresponding to the aforesaid equation insures that the electron stream becomes sufciently excited according to the radio frequency sigynal at the input such that an electromagnetic wave is re-excited in the output portion of the helix after encountering the attenuator. This re-excited wave in turn annalisa interacts with the modulated beam in a continnousrnanner as the wave. and the'V beam progress down the tube at practically the samevelocity in such a manner that the electromagnetic wavegains in, amplitude; Thelength of the output or lossless section of the helix should satisfy the equation G=AziECN-L, whereG equalsthe gain of the tube desired, A, is a coupling; loss figure relating the voltage associated with the increasing wave to the total. applied voltage, Bf is` a parameter associated with the increasing wave, CI is` the gain. parameter N is the length in, wavelengths of the propagatingV cutre, u is the fraction. of the cold loss which should be subtractedfrom the gainV of the increasing component of the propagated wave` and L is. the lossV in dbi per wavelength. Providing ay lengthf of input section greater than that corresponding to- CNO would result in little or, no addedl gain ir" the attenuation of they electromagnetic wave by the:` attenuation mediumis high enough to remove` most. of the electromagnetic energy. rThe length of the output section mayl be` adjusted within reason to provide the desired. gain for the wave coupled from the output of the propagating structure.

In certain instances and applications a: separate external source of potentialv and` the electrodes within the discharge device l may be omitted. the gas within discharge device l5 would be ionized by providing suflicient power inthe radio frequency fields of the waves propagated on the helix, such as occurs in TR devices.` This effect can be greatly enhanced. by utilizing the longitudinal magnetic field generated by magnet 5 if the magneticlieldxis the gyroresonant eld for the electrons of the gas at: the microwave frequency or" the waveson thehelix. The intiuence.l of gas plasma: on microwave energy? andthe gyroresonant effect therein is described in` greater detail: in the copending application of L. Goldstein etY al., Serial No: 232,1-48,.led lune i8, 195i.

Referring toFigs. 4 and 5, an alternative embodiment isillustrated-l including a cold cathode to establish the gas plasma for attenuation purposes. Device l5 includes an` annular-like envelope` including a metallic base material ZSinSertedlin a glass envelope 24E and secured thereto` by meansof a1 glass-to-metal seal at 25. The cold cathode material 25: is disposedon the inner surface of base metal-23 andhas applied' thereto-a pulsed potential from source4 27. In this embodiment, thefhelix. 4; functions essentially as a ground,` plane whereby electrons emitted from! material 26l will be accelerated back to material 26- for bombardment thereof toproduce secondary emissioni for ionization of the gas within` device 15. The cross section of device 1-5 is an` annular-like triangular configuration, the inner dimension'of the: gas device envelope being substantiallytangential to the` turns of helix 4 to dispose the gas plasma in a stronger field regionof: the field adjacent the helical'propagating structure.

To disposev thedevice l5 ina stronger fieldregionfof the` electromagnetic field adjacent helix 4 a structure as shown` in Fig.` 6-may be provided. Device 1S having an annular glass envelope` 16 has its inner wall 23y configured in a manner to-provide a spiral flute 29 to receive the turns of the helix` therein and thereby position the gas plasma in a` stronger field region of the field about helix 4. It is contemplated that the tluting of envelope 16 would engage the first turns of a helix and when revolved about the axis thereofl would thread itself onto the helix for appropriate positioning'.therealong. Theztapered ends of envelope` lrmay be sweated to a glass tubing la in a. manner to provide: a.A continuous rectilinear support for helix 4..

As is known, the maximum. electromagnetic eld on` a helical structure occurs` between the turns of the helix. Therefore,` if a gas tube or` gas plasma could `be positioned between adjacent turns of helix 4, the maximum absorption by the gas plasma would be achieved. Fig. 7 illus- In these instances,

trates an embodiment in; which the gas plasma is; posi.- tioned to be` intermediate adjacent turns. This. is? ac.- complished by'employing1aeapil-lary glass tube 30, which is.. interwoven with.V a metallic` helix-` 4 and containing` therein asuitable noble gas which maybe ionized by the radio frequency energy on the propagating structure alone or in combination. withthelongitudinal magnetic field, the intensity of which corresponds to the gy-roreso.- nant frequency of. the electronsf ofthe gasplasrnaV This structure could, of coursef. have electrodes` so disposed as to the gas within capilla-ry` tube 3.0.A The entire structure including: the.L helix 4 and capillary` tube. 30 would be supported for axial alignment withy the electron beam by means of non-conducting rods.- or tubing' 17h;`

Referring to Figs. 8 and 9, other embodiments of my gas discharge attenuator are shown for use with a traveling wave electron discharge device of thefhollow electron beam type wherein the gas discharge` devicel isdisposed axially within the helix* 4. The principle of absorption by a gas plasma is the same in these embodimentsy as itis in the previous embodiments. Fig. 8 illustrates that the helix l is supportedon rods 32 concentric with the hollow electron beam. Gas tube 3l' is inserted internally of the'rods 32 and as close to the maximum field region of the helical structure asis practical. It is contemplated that the gas tube. be concentrated ina. relativelyl short portion ofthe helical. propagating structurevbutnot necessarily limitedto `sucha concentration.

Fig. 9 illustrates diagrammatically the inclusionfof a gas attenuator 31 whichy is coextensive with` the` helical propagating structure, the outer surface of which is= employed to supporti` the helix 4` concentric with thezhollow electronbeam.

Fig. 10 illustrates the combination of a gas discharge device 33 similar to the discharge device 15.illust-rated in Fig. 4 and a traveling wave electron discharge` device` including a vacuum envelopesll havinga relatively small diameter enclosure utilized as thesupport` for helix 4,1as well as theA vacuum enclosure. The discharge device 33, for attenuating the waves` propagated` on helix 4,v is disposed about the vacuum envelope 3`4 andincorporatedas an integral part of the` metalpackaging shell` 35/ employed to protect the envelope 34 against breakage and shock hazards. Thus, a meanshas beeny discovered'whichtwill enablethe insertionlo a deliberate loss on the propagating structure which is effective when disposed. externally to the vacuum envelope ofthe travelingwavetubeprovided the discharge plasma is in juxtaposition. to the electromagnetic field about the-helix. With this arrangement, itwould be possible tor-easily replace the loss material or make adjustments thereon without opening, the vacuum envelope of the traveling wave tube4 itself.

The average radio frequency power. 'that can, be: absorbed by the gas discharge attenuator oftv this invention is generally limited by the material ofthe closure orI envelope, the electron density of the discharge plasma, the collision frequency of the electrons in the gas. and the proximity of the gas plasma to the radio frequency. fields surrounding the propagating structure. Absorption of average radio frequency powers in the order of several l0() watts would not be unreasonable. This method of producing the necessary cold lossof a helixor. other slow wave structure is more adaptable than present techniques to high power pulse tubes where the peak pulse powers may be large. ln addition, the gas tube attenuator can be air or liquid cooled to increase the power absorption limit of the device.

A successful reduction to practice employing the principles of this' invention utilized: a pulsed discharge in xenon gas atseveral mm. Hg pressure and produced l0 -to l5 db loss` at approximately 2600 megacycles. The

experimental condition under which the reduction to practice waslperformed was notoptimum since the discharge plasmaV was not very near the helix nor was the discharge located in a large portion of the radio frequency fields surrounding the helix. Experimentation with certain of the other noble gas indicated that absorption took place, but was 'not as high as compared to the loss achieved by employing xenon. It was further shown, however, that the absorption increases if the discharge exists over a longer length of helix and if it occurs nearer the helix. Standing wave measurements at the input to the helix proved the insertion loss provided by the gas discharge was due to absorption rather than reflection of the microwave energy by the plasma.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

l. ln a traveling wave electron discharge device having a slow wave propagating structure for transmission of radio frequency energy therealong and means to project a beam of electrons parallel to the axis of said propagating structure for interaction with the electromagnetic field of the radio frequency energy transmitted by said propagating structure; an attenuator disposed adjacent said propagating structure for absorption of radio frequency energy propagated therealong, said attenuator comprising a gaseous discharge device disclosed in juxtaposition to the electromagnetic field of said propagating structure whereby ionization of the gas of said gaseous discharge device attenuates the energy propagated along said propagating structure.

2. A device according to claim l, wherein the gas of said gaseous discharge device is selected from the group comprising helium, neon, argon, lcrypton and xenon.

3. A device according to claim 1, wherein the gas of said gaseous discharge device is xenon confined at several mm. Hg pressure.

4. A device according to claim l, wherein said propagating structure includes a helical transmission line and said gaseous discharge device includes a capillary tube interwoven with said helical transmission line for disposition between adjacent turns thereof thereby placing the ionized gas of said gaseous discharge device in the maximum field region of the electromagnetic field of said helical transmission line.

5. A device according to claim l, wherein said gaseous discharge device is disposed longitudinally of said propagating structure and the outer surface of said gaseous discharge device is tapered radially with respect to said propagating structure at the extremities thereof.

6. A device according to claim l, wherein said propagating structure has a substantially annular cross-section and said gaseous discharge device is disposed within said propagating structure.

7. A device according to claim 6, wherein said gaseous discharge device is cylindrical, the outer surface of which cooperates in supporting said propagating structure.

8. A device according to claim l, wherein said gaseous discharge device includes an envelope of annular-like ,cross-section disposed concentrically about said propagating structure.

9. A device according to claim 8, wherein the annularlike cross-section of said envelope is substantially circular.

l0. A device according to claim 8, wherein the annularlike cross-section of said envelope is substantially triangular for disposition of the ionized gas of said gaseous discharge device in closer proximity to the maximum field region of the electromagnetic field of said propagating structure.

ll. A device according to claim 8, wherein said propagating structure includes a helical transmission line and the inner surface of said envelope includes a spiral groove thereon for engagement with the turns of said helical transmission line to dispose the ionized gas of said gaseous discharge device in closer proximity to the maximum field region of the electromagnetic field of said helical transmission line.

l2. In a traveling wave electron discharge device having a slow wave propagating structure for transmission of radio frequency energy therealong, means to project a beam of electrons parallel to the axis of said propagating structure for interaction with the electromagnetic field of the radio frequency energy transmitted by said propagating structure, and a magnet concentric to and substantially coextensive with said propagating structure provide a longitudinal magnetic field to maintain the electrons of said beam parallel tti-the axis of said propagating structure for substantially the entire length thereof; an attenuator disposed adjacent said propagating structure for absorption of radio frequency energy propaga'ted therealong, said attenuator comprising a gaseous discharge device disposed in juxtaposition to the electromagnetic field of said propagating structure and means including the intensity of the magnetic field of said magnet to ioniZe the gas of said gaseous discharge device for maximum attenuation of the energy propagated along said propagating structure.

13. In a traveling wave electron discharge device having a conductor in the form of a helix for propagation of radio frequency energy therealong, dielectric material disposed about and substantially coextensive with said helix to provide a rectilinear propagating structure, means to project a beam of electrons axially of said helix for interaction with the electromagnetic field of the radio frequency energy propagated along said helix; an attenuator disposed adjacent said helix for absorption of radio frequency energy propagated therealong, said attenuator comprising an annular glass envelope disposed to surround said dielectric material and in a coupling relation with the electromagnetic field of said helix for a given axial length thereof, the extremities of said envelope being tapered radially with respect to said helix, a high electron density gas enclosed within said envelope, electrodes disposed within said envelope and a source of potential coupled to said electrodes to establish a difference of potential therebetween to ionize said gas for attenuation of the energy propagated along said helix.

i4. In a traveling wave electron discharge device having a conductor in the form of a helix for propagation of ratio frequency energy therealong dielectric material disposed about and substantially coextensive with said helix to provide a rectilinear propagating structure, means to project a beam of electrons axially of said helix for interaction with the electromagnetic field of the radio frequency energy propagated along said helix; an attenuator disposed adjacent said helix for absorption of radio frequency energy propagated therealong, said attenuator comprising an envelope of annular-like cross-section disposed to surround said dielectric material and in a coupling relation with the electromagnetic field of said helix for a given axial length thereof, a high electron density gas enclosed within said envelope, said envelope including in the outer wal-l thereof a central portion disposed between two glass end portions, said central portion including a metallic base material coated with a suitable cold-cathode material sealed to each of said end portions, said end portions being tapered radially with respect to said helix, and a source of pulsed potential coupled to said cold-cathode material which in cooperation with the direct current potential of said helix ionizes said gas by secondary electron emission for attenuation of the energy propagated along said helix.

l5. in a traveling wave electron discharge device having a conductor in the form of a helix for propagation of radio frequency energy therealong, input means to couple radio frequency energy to the input of said helix, output means to couple radio frequency energy from the output of said helix, dielectric material disposed about said helix extending from the input end and the output end of said helix to a given central portion of said helix to co operate in providing a rectilinear propagating structure, a magnet concentric to and substantially coextensive with said propagating structure to provide a longitudinal magnetic iield to maintain the electrons of said beam parallel to the axis of said propagating structure for substantially the entire length thereof, means to project a beam of electrons axially of said helix for interaction with the electromagnetic tield of the radio frequency energy propagated along said helix; an attenuator disposed in said given central portion for absorption of radio frequency energy propagated therealong, said attenuator comprising an an nular glass envelope disposed to be coextensive with said given central portion and in a coupling relation with the electromagnetic field of said helix, said envelope having the ends thereof tapered radially with respect to said helix and the inner surface thereof grooved in the form of a spiral to engage the turns of said helix for cooperation with said dielectric material to provide a rectilinear structure and increase the coupling to said electromagnetic field and a high electron density gas enclosed within said envelope whereby the energy of the radio frequency wave and the longitudinal magnetic field of said magnet cooperate to ionize said gas for attenuation of the energy propogated along said helix.

16. In a traveling wave electron discharge device having a metallic helix for propagation of radio frequency energy therealong, dielectric material disposed about and substantially coextensive with said metallic helix to provide a rectilinear propagating structure, means to project a o beam of electrons axially of said metallic helix for inter action with the electromagnetic field of the radio frequency energy propagated along said metallic helix; an attenuator disposed adjacent said metallic helix for absorption of radio frequency energy propagated therealong, said attenuator comprising a capillary tube in the form or a glass helix disposed to be intermediate the turns of said metallic helix having the same helical diameter as said metallic helix, and a high electron density gas enclosed in said tube whereby the ionization of said gas provides maximum attenuation of the energy propagated on said metallic helix.

17. In a traveling Wave electron discharge device having a conductor in the form of a helix for propagation of radio frequency energy therealong, dielectric material disposed within and substantially coextensive with said heiix to provide a rectilinear propagating structure, means to project a hollow beam of electrons parallel to the axis of said helix for interaction with the electromagnetic field of the radio frequency energy propagated along said helix, said helix being disposed within said beam of electrons; an attenuator disposed adjacent said helix for absorption of radio frequency energy propagated therealong, said attenuator comprising a cylindrical envelope disposed within said dielectric material to be in a coupling relation with the electromagnetic field of said helix for a given axial length thereof, the extremities of said envelope being tapered radially with respect to said helix, and a high electron density gas enclosed within said tube whereby the ionization of said gas provides attenuation of the energy propagated along said helix.

i8. In a traveling Wave electron discharge device having conductor in the form of a helix for propagation of radio frequency energy therealong, means to project a holiow beam of electrons parallel to the axis of said helix for interaction with the electromagnetic hield of the radio frequency energy propagated along said helix, said helix being disposed within said beam of electrons; au attenuator disposed adjacent said helix for absorption of radio frequency energy propagated therealong, said attenuator comprising a cylindrical envelope disposed within said dielectric material and in a coupling relation with the electromagnetic field of said helix for a given axial length thereof, the extremities of said envelope being tapered radially with respect to said helix, and a high electron density gas enclosed in said tube whereby the ionization of said gas provides attenuation of the energy propagated along said helix, said envelope cooperating to support said helix over said given axial length.

No references cited. 

